Ante-Nicene Fathers, Vol III:
Tertullian: Part I: The Charge of Worshipping the Sun Met by a Retort.

Others, with greater regard to good manners, it must be confessed, suppose that the sun is the god of the Christians, because it is a well-known fact that we pray towards the east, or because we make Sunday a day of festivity. What then? Do you do less than this? Do not many among you, with an affectation of sometimes worshipping the heavenly bodies likewise, move your lips in the direction of the sunrise? It is you, at all events, who have even admitted the sun into the calendar of the week; and you have selected its day, 673
in preference to the preceding day 674
as the most suitable in the week 675
for either an entire abstinence from the bath, or for its postponement until the evening, or for taking rest and for banqueting. By resorting to these customs, you deliberately deviate from your own religious rites to those of strangers. For the Jewish feasts on the Sabbath and “the Purification,” 676
and Jewish also are the ceremonies of the lamps, 677
and the fasts of unleavened bread, and the “littoral prayers,” 678
all which institutions and practices are of course foreign from your gods. Wherefore, that I may return from this digression, you who reproach us with the sun and Sunday should consider your proximity to us. We are not far off from your Saturn and your days of rest.